Enhancing Encoding of a Motor Memory in the Primary Motor Cortex By Cortical Stimulation

1 Human Cortical Physiology Section, National Institute of Neurological Disorders and Stroke, 20892-1428 2 Biometry and Field Studies Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-9135 Submitted 27 October 2003; accepted in final form 27 December 2003 Motor training results in encoding of motor memories, a form of use-dependent plasticity. Here we tested the hypothesis that transcranial magnetic stimulation (TMS) synchronously applied to a motor cortex engaged in a motor training task could enhance this plastic process. Healthy volunteers were studied in four sessions: training consisting of performance of directionally specific voluntary thumb movements ( Train alone ), training with TMS delivered during the execution of the training movement in a strictly temporal relationship to the motor cortex contralateral ( Train + TMS synchronous contra ) and ipsilateral ( Train + TMS synchronous ipsi ) to the training hand, and training with TMS delivered asynchronous to the training movement to the motor cortex contralateral to the training hand ( Train + TMS asynchronous contra ). Train alone, Train + TMS synchronous contra , and Train + TMS asynchronous contra but not Train + TMS synchronous ipsi elicited a clear motor memory. The longevity of the encoded memory was significantly enhanced by Train + TMS synchronous contra when compared with Train alone and Train + TMS asynchronous contra . Therefore use-dependent encoding of a motor memory can be enhanced by synchronous Hebbian stimulation of the motor cortex that drives the training task and reduced by stimulation of the homologous ipsilateral motor cortex, a result relevant for studies of cognitive and physical rehabilitation. Present address and address for reprint requests and other correspondence: C. Bütefisch, Neurological Therapeutic Center, Institut at the Heinrich-Heine University, Hohensandweg 37, 40591 Düsseldorf, Germany (E-mail: cathrin.buetefisch{at}uni-duesseldorf.de ).